I'm not sure how to answer you. Not criticizing, just saying I don't really understand what you are asking. I'll try anyway...
First, it's your railroad if you are not modelling prototypes. So, you can do as you please. In real life, passenger consists were made up and split, or parcelled out as the need arose. Two cars from a train between St. Louis and Chicago would be set out for a train running west, once the train reached Chicago, and sent to their destination west of Chicago. When making up the train in St. Louis, they'd go through their servicability roster of needed and available cars, including those that had to be returned to their parent railroad, and marshall them on a side track. Dining cars, especially, were set in and out for cleaning and provisioning at a dock, and then placed into service later that day or evening. You could do that.
As for crews, they carried their meals in lunch boxes and ate on the fly. Peeing was done over the side, just like when fishing. In the event of a need to evacuate one's bowels, that was most comfortably held until the next substantial station stop, and done in a mad dash. If one was held up, and late as a result, the engineers had no qualms about upping their between-stop speeds for the next two or three legs to make up time. A story in Trains magazine in the early 90's tells of a dusty PRR Duplex that was pressed into service at the last minute. It got behind, and during a 40 mile leg the engineer had the beast well up over 125 mph, making up nine minutes.
Otherwise, it, too was over the side, or done in a honey bucket behind a privacy curtain. Depending on local custom.
Edit - I just re-read your question...do you mean during Ops Sessions? If so, I am sorry for what I replied above...won't be of much help to you.
-Crandell